Spongy brake pedal after steep downhill

[TOR]

I did a couple of tracks in the Pyrenees ranges in Victoria over Easter. Doing a long downhill descent in 1st LOW, put the foot on the brakes to stop and nothing much happened, quick couple of pumps and it was back to being ok. I had to do this a few times to keep pressure there when I need to stop. Definitely a little unnerving.

Now i wasn't really using the brakes at all during descent so they shouldn't have heated up or anything. Could this be as simple as some air in the system finding its way somewhere when the nose of the car was pointed down for so long? I'm definitely going to bleed and change the brake fluid, but is there something else to look out for?

[bee utey]

I'd be looking for loose wheel bearings.

[roverrescue]

Cracked and leaking booster?

S

[TOR]

Why the wheel bearings?

Would the leaky booster make the pedal feel soft though? I just thought it would be harder to push?

[JDNSW]

Loose wheel bearings, plus the disc moving side to side, push the shoes back, so when you apply the brakes the shoes need to move further. Does not need much before the amount of fluid available from one push of the pedal is reached.

I agree this is the most likely issue - the descent, presumably with the car rocking side to side, could easily have this effect, where it did not become apparent with less of this rocking on the highway.

Another thing to check is that you have not had a rear brake failure, due to a broken line etc, and the extra movement was just pushing the equaliser all the way over.

[TOR]

Thanks for the explanation, makes perfect sense. I did have to nip up a loose wheel bearing before I left for the trip. Is it good practice to replace all wheel bearings together?

[rick130]

Even a corrugated road can have the pistons retract a wee bit in the calipers.
I was in the habit of a confidence tap on the brake before actually hitting the pedal on dirt roads, it just brings the pads up to the disc.
Endurance race car drivers used to do this at the end of a long straight with their left foot for the same reason.

Slider calipers as fitted to most modern cars (e.g., the D2) don't do this as the caliper floats with disc movement.

[JDNSW]

Thanks for the explanation, makes perfect sense. I did have to nip up a loose wheel bearing before I left for the trip. Is it good practice to replace all wheel bearings together?

Oil fed bearings are very long lasting (three out of four of mine are original at over 600,000km), so my view would be to replace them when needed.

[rick130]

Cracked and leaking booster?

SThat'll give a long but hard pedal Steve.
And you aren't able to bring the pedal back with a few taps.

[discorevy]

Another possibility is master cylinder bypassing fluid or leaking fluid from brake line , caliper etc. Is level OK?
Try applying the brake with engine running while stationary, if the pedal is OK then recheck wheel bearing play